Apparatus for continuous digesting



Feb. 23, 1932. G. c. GRE-ss ET AL VAPPARATUS FOR CONTINUOUS DIGESTING Filed July 28, 1928 A TTORNEYS.

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lukrml xZSr. Fila Patented Feb. 23, 1932 UNT STATES PATENT OFFC GEORGE C. GRESS, F SPRINGFIELD, AND RAYMOND T. KERN, OF LEOMINSTER, MASSA- CHUSETTS, ASSIG-NORS TG THE VFEBE3;`tlw)]]'J CGR-PORATION, OF INDIAN ORCHARD, MASSACHUSETTS, A CORPORATON 0E" MASSACHUSETTS APPARATUS FOR CGNTINUUS DIGESTNG- Application filed July 28, 1928. Serial No. 295,903.

This invention relates to improvements in the method and apparatus for digesting nitrocellulose and the like.

ln the cellulose industry as one step in the' manufacturing of pyroxylin the cooking or digesting of the cellulose material is an important consideration, the importance of which need not be hereinv referred to in detail, except to stat-e that the present practice calls for a digesting or cooking operation which will produce material of extremely high qualities.

One common method of digesting such material is as follows: llhe material is confined in closed vats or kettles for a number of hours and is digested by a cooking liquid which in order to produce the best results is under considerable pressure and maintained at a relatively high temperature. The pressure and temperature conditions facilitate the desired digesting operation and is accomplished by the admission of high pressure steam directly to the liquid and matei rial being digested.

Many serious objections and disadvantages are presented in connection with the method and apparatus just described which will be referred to briefly in order to facilitate a clear understanding of the novel features and advantages of the present invention.

In order to obtain the best results the temperature of the cooking liquid should be relatively high, as for instance in the neighborhood of 270 degrees F ah. and the material should be submerged at all times. TWith this temperature condition there is a tendency for the cooking liquid to vaporize so that the nitro-cellulose material is not completely submerged in a liquid at all times during the cooking operation. lt is a well-known fact that explosive gases are generated by the decomposition reaction, which gases are more active when the system is filled with vapor than when the cooking liquid is in a liquid state. Thus the tendency of the liquid to vaporize not only aects the actual digesting operation but brings about an extremely dangerous condition.

Also in connection with the apparatus above described it is necessary to first charge or load the vat for a cooking operation, and then after the digesting it is unloaded which not only entails labor and expense but the equipment itself is far too costly for the results which are obtained thereby.

rEhe principal objects of this invention are the provision of a method of and apparatus for cooking or digesting nitro-cellulose and the 'like wherein the cooking liquid is maintained in a liquid state and at the desired relatively high temperature throughout the digesting operation so as to obviate the hazard caused by explosive gases generated by the operation and at the same time bring about a more thorough and eiiicient digesting of the material. This is accomplished according to one novel feature of the invention by providing a novel process and apparatus wherein the material being digested is carried in a cooking fluid through a system of novel form wherein the temperature or temperatures of the liquid are maintained at the desired Working ranges by the external application of heat or at least without the admission of steam directly into the system.

According to a further feature of the invention means are provided for maintaining a pressure differential in the system so as to overcome any tendency of the cooking liquid to vaporize, in which condition it would not function as a conveying medium, and would bring about the objectionable conditions previously referred to.

The novel features of the invention may be carried out in various Ways and by means of various forms'of apparatus but for purposes of disclosure the invention will be described in connection with the accompanying drawing which shows a form of apparatus at present preferred for carrying out the invention.

ln the drawing the figure represents in a diagrammatic way one form of an apparatus for carrying out the invention.

Referring to the drawing in detail the invention will now be described. S represents a stock chest or storage tank for holding carrying liquid and undigested material such as nitro-cellulose and is provided with a discharge outlet in the lower side thereof. Tanks P, H, D and C are provided which enclose coils of piping or conduits P', H', D and C respectively. r'hese coils have their adjacent ends connected by pipes 2, l and G, while the outer ends of the coils P and C are connected to the discharge side of a circulating pump 8 and a discharge outlet l() respectively. rlhe chest S is suitably connected by a pipe to the suction side of the pump 8 so thatJ the pump may circulate liquid and the material to be digested through the various coils and subsequently discharge the same through the pipe l0. To supply the carrying and digesting liquid for the system a tank or tanks such as T may be provided which has a discharge outlet controlled by a valve for delivering suitable liquid to the chest S of the system.

rlhe tanks P, H and D enclosing the inter-- connected coils are arranged and adapted to function as jackets for the coils so that the material and liquid therein may be heated to the desired temperatures. This may be accomplished in one way by the admission of steam through the pipes l2, la and 16 as is indicated while valves l2', l-l and 1G in the pipe lines as shown may be utilized to regulate the liow of steam to the respective tanks. Other valves l2, 14 and 16, which may be thermostatically controlled by the thermostats T in the piping connections 2, l and 6, may operate to automatically control the flow of steam and thereby control the resulting temperatures in the several tanks.

The coil and tank C and C Will for convenience be referred to as the cooling` unit and some suitable cooling medium such as relatively cold water may be delivered thereto by means of the pipe 18 while the liow of water through the same may be controlled by a valve 18 and/or by a thermostatically controlled valve indicated by 18 which is controlled by thermostat TC The relative sizes, length and capacity of the coils, their connections and the discharge outlet may vary within wide limits as may the size or capacity of the pump for circulating the carrying fluid and material. To obtain best results however the apparatus will be arranged so that with certain relative predetermined temperature conditions present in the different tanks and with a certain rate of iow the material will be thoroughly and adequately digested while it circulates through the system and is finally discharged in a suitable condition for subsequent manufacturing operations.

lt will be understood that the relative temperatures employed inrconnection with the several coils may of course be varied as is desired. The mode of operation of the apparatus thus far outlined will now be described with reference to certain conditions which have not only been found to be practical but which produces a very high grade product in a most economical and eliicient manner. For instance the carrying fluid and nitro-cellulose material may be discharged by the pump into the coil P of the tank P, which may be called a low temperature preheating unit, at room temperature say about 50 degrees F ah. and the temperature in this tank may be sutlicient by the proper admission and control of steam to raise the temperature to approximately 200 degrees Fah.

The temperature in the tank H may be controlled orregulated so as to heat the liquid and material to a temperature of say 320 degrees which may be substantially equal to that of the temperature in the tank D. This may be called a high temperature pre-heating step. rfhe raising of the temperature by the preheating steps brings about a desirable condition in that the liquid and material arrive at the coil in tank D at a temperature which is substantially equal to that which is maintained therein and which desired to accomplish the best results. The coil D is preferably of greater length than the pre-heating coils in order that the material and liquid may be subjected to this relatively higher digesting temperature for a sufficient length of time to bring about the desired cooking action. rShe temperature in the cooling tank C may be maintained at any temperature required to bring about the cooling action and as before stated may be accomplished by the proper control and supplying of a cooling medium such as water.

ln order to maintain the carrying liquid in the liquid state while operating at the relatively hi gh pressures referred to, it is necessary to .superimpose on the pressure in the system additional pressure. That is to say, in order to prevent a vaporiZing tendency at the high temperature referred to say of 270 degrees Fall. or more, it is necessary to maintain a pressure in the system which is somewhat greater than the pressure which would ordinarily prevail with the temperature stated. To attain this, the following is provided:

A valve V is provided in the discharge l so as to control the flow of digested material and liquid. This valve is preferably of the type commonly known as the false water level type which has a valve plug movable towards and away from a seat that is actuated by a float 2O in a closed tank 22. A closed tank E for carrying a liquid such water has an outlet 24 in communication with the discharge and is in communication with the tank 22 so that pressure conditions may be alike in both tanks.

Aa pressure is delivered to the tank E by means of any suitable compressor or pump A which pressure may be regulated or controlled by a suitable valve or valves in a connection 26 between the tank and pump. lilith the arrangement described pressure of various desired values may be delivered to the tank and system. If for any reason the pressure in the system decreases for instance the water level in the tanks E and 22 lowers so that the valve V is moved towards a closed position to thereby restrict the discharge oritice. An increase in pressure in the system of course causes the valve V to open to relieve the pressure and thus the pressure throughout the system is maintained at a desired value with the additional advantage that the said pressure may be maintained at a value which is greater than that at which the liquid vaporizes at the particular operating temperature.

From the foregoing it will be observed that there is provided a novel process and apparatus for digesting nitro-cellulose or other materials which according to the novel features thereof functions so that the material is carried by a suitable cooking medium through various heating and cooling imits to the end that undigested material delivered at one point is discharged as a digested material at another. As a further feature it will be observed vthat by means of the supplying of a differential pressure to overcome any tendency of the carrying liquid to vaporize it is possible to maintain the liquid at relatively high temperatures and at a uniform pressure to the end that an efficient and desirable cooking operation is performed.

The invention may be practiced in various ways and by means of various forms of apparatus without departing from the spirit and scope of the invention, therefore we prefer to be limited, if at all, by the appended claims rather than by the foregoing description.

lVhat is claimed is:

l. An apparatus for digesting nitro-cellulose and the like comprising in combination, a conduit, a valve in said conduit for opening and closing the passage therethrough, a closed liquid tank above said conduit having a float connected to said valve to operate the same whereby as the level of liquid in said tank rises and falls the valve is closed and opened, a second closed tank connected to said first-named tank and to said conduit adjacent said valve whereby as the level of liquid in said tank is raised and lowered by an increase or decrease in pressure in said conduit the float in said first-named tank is operated.

2. An apparatus for digesting nitro-cellulose and the like comprising in combination, a conduit, a false water level valve at the outlet end of said conduit for opening and closing the same, separate closed tanks for liquid above said valve, a float in one of said tanks connected to said valve and operable in raising and lowering movements to close and open the same, the other of said tanks being sure prevailing in said conduits to open and close said valve and thereby maintain said pressure in the conduit uniformly.

GEORGE C. GRESS. RAYMOND T. KERN. 

